In an unprecedented study, a team of researchers measured the extent of coral bleaching across tropical regions spanning over four decades. The experts established that these bleaching events are now occurring more frequently and are also significantly more widespread.
Professor Terry Hughes is the director of the ARC Centre of Excellence for Coral Reef Studies and lead author of the research.
“The time between bleaching events at each location has diminished five-fold in the past 3-4 decades, from once every 25-30 years in the early 1980s to an average of just once every six years since 2010,” said Hughes.
The researchers are reporting that the current rate of coral bleaching is capable of completely wiping out coral reefs and threatens the livelihoods of millions of people.
“Before the 1980s, mass bleaching of corals was unheard of, even during strong El Niño conditions, but now repeated bouts of regional-scale bleaching and mass mortality of corals has become the new normal around the world as temperatures continue to rise,” said Hughes.
According to the study, coral bleaching only occurred locally before the 1980s. But now, global warming has triggered extraordinarily widespread bleaching events that coincide with El Nino Southern Oscillation (ENSO) cycles.
The researchers found that tropical seawater temperatures are warmer today during cooler than average La Niña events than they were 40 years ago during the unusually warm El Niño conditions.
“Coral bleaching is a stress response caused by exposure of coral reefs to elevated ocean temperatures,” explained co-author Professor Andrew Baird. “When bleaching is severe and prolonged, many of the corals die. It takes at least a decade to replace even the fastest-growing species.”
Study co-author Dr. C. Mark Eakin of the National Oceanic & Atmospheric Administration (NOAA) said that coral reefs have now entered into an era where human activities are dominant, known as the Anthropocene.
“The climate has warmed rapidly in the past 50 years, first making El Niños dangerous for corals, and now we’re seeing the emergence of bleaching in every hot summer,” said Dr. Eaken.
The Great Barrier Reef has now bleached four times since 1998, including two consecutive bleaching events in 2016 and 2017, which caused severe damage.
“We hope our stark results will help spur on the stronger action needed to reduce greenhouse gases in Australia, the United States and elsewhere,” said Professor Hughes.
The study is published today in the journal Science.
By Chrissy Sexton, Earth.com Staff Writer